This invention is related to varactor television tuning systems which vary tuning frequency by a change in the application of voltage to a varactor diode tuning device. More specifically, it relates to the form of varactor television tuning systems which selectively tune to desired television channels according to a predetermined channel program sequence which has been stored in a memory.
A versatile memory tuning system is completely disclosed and claimed in application Ser. No. 466,579, filed May 3, 1974, now U.S. Pat. No. 3,946,319 issued Mar. 23, 1976, in the names of John Ma & Akio Tanaka and entitled "All Electronic Digital Tuner System with Memory" and assigned to the assignee of the present application. The memory may be programmed in any desired sequence to provide sequential tuning among a selected group of channels. Storage locations are accessed to some convenient speed and tuning information is stored at individual locations. The advantages of such a tuning system with a memory are readily apparent since the viewer need sequence through only desired channels. The memory has sufficient capacity to hold the digits of the desired channel number, normally in binary encoded decimal form. The speed at which memory locations are accessed and the stored tuning information extracted is so rapid that the change of stored selections appears to be instantaneous.
A characteristic of all memory tuning systems is that they normally have two modes of operation, a program mode in which channel selections are made and an operate mode in which channel selections are recalled. With varactor diode tuners, channel selection involves supplying a proper DC tuning voltage to the tuner. The mechanism for supplying the proper voltages may range from digitally accessed adjustable potentiometers to binary memories for storing channel numbers. In the operate mode the viewer then only sweeps through the limited number of preselected channel numbers for tuning to the desired channel.
Application Ser. No. 457,010, filed Apr. 1, 1974, now U.S. Pat. No. 3,931,579 issued Jan. 6, 1976, in the name of Akio Tanaka entitled "Digital Signal Seeking Tuning System" and assigned to the assignee of the present application discloses a television tuning system which includes channel counters operating sequentially to generate desired channel numbers. As each channel number is generated the system responds by tuning to the frequency location corresponding to the channel number. The system also utilizes signal recognition means to determine if a receivable signal is present at that frequency location and stops additional channel number generation until reactivated by the viewer. This use of channel counters to generate channel number information greatly simplifies the tuning system for the viewer, but no provision is made for a memory to store selected information.
A memory of the type which could store selected tuning information could be added to a channel counter system to provide for a convenient method of selecting from all possible channels only those channels which the viewer desires. Such a memory is described in the related application, Ser. No. 621,911. As with all memory systems, in the program mode the operator selects among all available channels and creates the sequence of desired channels available in his locations for subsequent viewing. In the operate mode the viewer chooses from those selected channels the particular channel he wishes to view.
With this system a single device, the counter, both generates the tuning information and accesses the memory location to determine if it has been selected. A problem arises with a single speed system in that when making selections in the program mode, all channels cannot be sequentially generated in the same time. The time required for any individual would depend upon the starting count remaining on the counter. But there are only 12 possible VHF channels some of which may be numerically adjacent whereas in the UHF band there are 70 possible channels and in most locations broadcasting UHF channels are normally separated by six channel numbers.
VHF channels are generally available in all locations and therefore most viewers would normally select some channels numbered 13 or less. With a single speed counter operating to provide time for viewer recognition of channel numbers, the time required to generate the larger number and more widely displaced UHF channel numbers would be annoyingly long. Similarly, a fast counter permitting easy access to all UHF channels may well be too fast for making VHF selections without difficulty. The present invention memory tuning system employs counters and includes apparatus for controlling the speed at which the counters advance to generate channel number information to produce two speeds in the program mode. The viewer can control both direction and speed of the sequential counter advancement. The access time to channels is reduced since a fast speed can be used to skip unwanted channels and a slow speed can be used with channel number recognition to make the selection. Thus, the viewer can make comfortable selections of any channels during the program mode.